(1) Field of the Invention
This invention relates to an impact-resistant styrenic polymer resin composition having well-balanced impact resistance and gloss, and a process for making the impact-resistant styrenic polymer resin composition.
(2) Description of the Related Art
Impact-resistant styrenic polymer resin compositions are made by a process wherein a solution of a toughening agent such as polybutadiene in a styrenic monomer is subjected to a bulk polymerization or a bulk-suspension polymerization. The resulting impact-resistant styrenic polymer resin compositions have an improved impact resistance but a poor surface gloss, as compared with polystyrene. To enhance the surface gloss of the impact-resistant styrenic polymer resin compositions, a process was proposed wherein polybutadiene having a relatively low viscosity is used (JP-A-51-131590). The surface gloss obtained by this process is still not satisfactory. Another process was proposed wherein a styrene/butadiene block copolymer is used (JP-B-42-17492, JP-B-48-18594 and JP-B-60-57443). Impact-resistant styrenic polymer resin compositions made by this process are characterized in that rubber particles dispersed in the resin compositions have a very small particle diameter, and thus, the surface gloss is improved, but the impact resistance is reduced. Further, the styrene/butadiene block copolymer is easily reduced to powder and generally has poor handling properties, as compared with conventional rubbery polymers, such as polybutadiene.
A further process was proposed wherein a styrene/butadiene block copolymer having specific styrene blocks is used (JP-A-64-74208 and JP-A-64-74209). The use of such block copolymer results in somewhat improved handling properties, but the impact resistance of the resulting resin composition is still not satisfactory. Still another process was proposed wherein polybutadiene is used in combination with a minor amount of a styrene/butadiene block copolymer (JP-A-56-2310). The impact resistance is improved by this process, but the surface gloss is approximately similar to those of the conventional impact-resistant styrenic polymer resin compositions.